简述：vue 的watch的监听使用的几种写法。常用第4中写法。 

一、$route监听路由跳转

前提：当需要前端监听路由跳转的时候，一般写在App.vue入口

//App.vue
//vue2、uniapp写法
watch: {
    $route(to, from) {
      if (hasPermission(to.path)) {
        this.$store.commit("setIisShipGuid", false);
      } else {
        this.$store.commit("setIisShipGuid", true);
      }
    },
  },

二、监听store中的某些变量

//vue2、uniapp写法 
watch: {
    "$store.state.isShipGuid": {
      handler(newVal, oldVal) {
        if (newVal !== oldVal) {
          this.isShipGuid = newVal;
        }
      },
      immediate: true,
      deep: true,
    },
  },

//vue3 setup写法
watch(
  () => store.selectShip.mmsi,
  (oldNum, newNum) => {
    if (oldNum != newNum) {
      try {
        cabin.getEngineRoomMenu(store.selectShip.mmsi);
      } catch (error) {
        cabin.getEngineRoomMenu(store.selectShip.mmsi);
      }
    }
  },
  { immediate: true, deep: true }
);

三、自定义组件内部监听传参

//封装的一个图表组件。监听传参
//vue2、uniapp
export default {
  props: {
    height: {
      type: String,
      default: "100%",
    },
    width: {
      type: String,
      default: "100%",
    },
    echartsId: {
      type: String,
      required: true,
    },
    series: {
      type: Array,
      default: [],
    },
    title: {
      type: Object,
      default: null,
    },
  },
  //监听传参
  watch: {
    myOption: function (newVal) {
      if (newVal) {
        console.log(
          "=================================================================="
        );
        this.myCharts.clear();
        this.init();
      }
    },
    series: function (newVal) {
      if (newVal) {
        console.log(
          "=================================================================="
        );
        this.myCharts.clear();
        this.init();
      }
    },
  },
}

//vue3写法
//监听多个参数的数组的写法
watch(
  [() => props.modelValue, () => data.defaultFileList],
  ([newValue1, newValue2]) => {
    console.log("newValue1", newValue1, "newValue2", newValue2);
  },
  { deep: true }
);

四、监听单个页面组件内部的data()

(一)、监听某一个对象

 data() {
    return {
      isActive: 0,
 }}
//vue2、uniapp写法
//vue2在单个页面组件内部，只能有一个watch
//vue3在单个页面组件内部，可以有多个watch
  watch: {
    isActive(newval) {
      this.currentIndex = newval;
    },
    "$store.state.mmsi": {
      handler(newVal, oldVal) {
        if (newVal !== oldVal) {
          this.mmsi = newVal;
          this.getEngineRoomMenu(this.mmsi);
        }
      },
      immediate: true,
      deep: true,
    },
  },

(二)、监听一个对象的某一个属性

//vue、uniapp写法
watch: {
	'search.name': {
		handler() {
			// todo
		},
	}
}
或者：
computed: {
    getName: function() {
    	return this.search.name
    }
}
watch: {
     getName: {
         handler: function() {
            //todo 
         },
     }
}

 

const data = reactive({
  ruleForm: {
    param: {},
  },
)
//vue3写法
watch(
  () => data.ruleForm.param.publishType,
  (newName, oldName) => {
    if (newName === 1) {
      data.useridsList_display = true;
    } else if (newName === 0) {
      data.ruleForm.param.useridsList = [];
      data.useridsList_display = false;
    }
  },
  {
    immediate: true,
    deep: true,
  }
);

其它，